Blue phases are types of liquid crystal phases that appear in a temperature range between a chiral nematic phase and an isotropic liquid phase. Because blue phases have a three-dimensional cubic structure with lattice periods of several hundred nanometres, they exhibit selective Bragg reflections in the range of visible light corresponding to the cubic lattice. From the viewpoint of applications, although blue phases are of interest for fast light modulators or tunable photonic crystals, the very narrow temperature range, usually less than a few kelvin, within which blue phases exist has always been a problem. Here we show the stabilization of blue phases over a temperature range of more than 60 K including room temperature (260-326 K). Furthermore, we demonstrate an electro-optical switching with a response time of the order of 10(-4) s for the stabilized blue phases at room temperature.

The film thickness dependence of surface structure for immiscible polystyrene/poly(methyl methacrylate) (PS/PMMA) films was investigated on the basis of atomic force microscopic observation and X-ray photoelectron spectroscopic measurement. In the case of the PS/PMMA film of 25 μm thickness, the air−polymer interfacial region was covered with a PS rich overlayer due to its lower surface free energy compared with that of PMMA and a well-defined macroscopic phase-separated structure was formed in the bulk phase. Also, in the case of the PS/PMMA thin film of 100 nm thickness, the phase-separated structure, in which the PMMA rich domains separated out of the PS rich matrix, formed at the film surface. The formation of the surface structure for the PS/PMMA thin film can be attributed to either the chain conformation or chain aggregation structure being frozen at the air−polymer interfacial region before the formation of a PS rich overlayer due to the fairly fast evaporation of solvent molecules. On the other hand, the two-dimensional PS/PMMA ultrathin film of 10.2 nm thickness did not show distinct phase-separated structure. When the film thickness became thinner than 10.2 nm, the two-dimensional PS/PMMA ultrathin film of 6.7 nm thickness showed fine and distinct phase-separated structure with the domain size of a few hundred nanometers. This structure can be designated as “mesoscopic phase-separated structure”. The surface phase state for the two-dimensional PS/PMMA ultrathin films can be explained by the film thickness dependence of both the interaction parameter and the degree of entanglement among polymer chains.

Forced modulation scanning force microscopic (SFM) and lateral force microscopic (LFM) measurements of the monodisperse polystyrene (PS) films were carried out at 293 K in order to reveal surface molecular motion. Surface dynamic storage modulus, E′, and surface loss tangent, tan δ, of the monodisperse PS films were evaluated on the basis of forced modulation SFM measurement. It was revealed that the magnitudes of surface E′ and surface tan δ were lower and higher than those for its bulk state, respectively, in the case of the number-average molecular weight (Mn) lower than 26.6k. Based on forced modulation SFM measurements, the surface of the PS film with Mn lower than 26.6k was in a glass-rubber transition state even at 293 K, in spite of that the bulk Tg was far above 293 K. LFM measurements for the PS films revealed that the magnitude of lateral force was dependent on the scanning rate of the cantilever tip in the case of Mn lower than 40.4k. The scanning rate dependence of lateral force appeared in the case that the surface of the PS film was in a glass-rubber transition state. LFM results agreed well with forced modulation SFM ones if the scanning rate of the cantilever tip for LFM measurement was converted to the measuring frequency for forced modulation SFM measurement. The active thermal molecular motion on the polymeric surface was explained by the excess free volume induced due to the surface localization of chain end groups. The surface enrichment of chain end groups was confirmed by dynamic secondary ion mass spectroscopic measurement.

Series of polyelectrolyte−surfactant complexes, DNA−cationic surfactant complexes (cetyltrimethylammonium, cetylpyridinium, and cetylbenzyldimethylammonium), and their self-assembled bulk film materials were prepared on a large scale. Circular dichroism (CD) analysis indicated that the right-handed double helix structure of DNA was retained in these bulk film materials. TGA analysis suggested that 4 molecules of water were required to retain the B-type conformation of the DNA helix in the self-assembled bulk film materials. In addition, it revealed that DNA and the DNA−surfactant complex film materials were thermostable up to as high as 180 °C. Thermodynamical analysis indicated that these film materials were thermo-extensive over a temperature range from 100 to 148 °C. The DNA conformation in the supramolecular complex films can be reversibly tuned by changing the environmental humidity. Film formation was found to occur by self-assembly and self-organization with evaporation of solvent molecules. Various functional dyes such as laser dye, NLO dye, and photochromic dye could easily be incorporated in the self-assembled supramolecular complex films as adducts. Studies of the induced CD spectra demonstrated that 4[4-(dimethylamino)styryl]-1-dococylpyridinium (DMASDPB) could orient on the chiral nanotemplates of DNA in the self-assembled films. UV−vis analysis indicated that these film materials have high transparency from 300 to about 1000 nm. These self-assembled functional-dye-containing DNA−surfactant complex materials, with good processability for multilayer integration into large-area devices, will have promising applications in molecular optical and molecular optoelectronic fields.

Optical shutters whose operation is based on the Kerr effect, which is a quadratic electro-optic effect generated in optically isotropic substances, have extremely fast response times. However, the magnitude of the induced birefringence in conventional Kerr materials is too small for them to be used in flat-panel displays. We show that a polymer-stabilized blue phase has a Kerr constant which is about 170 times larger than that of nitrobenzene. We also demonstrate microsecond electro-optical switching over a wide temperature range for flat Kerr cells containing the polymer-stabilized blue phase. These achievements can contribute to providing fast-response flat-panel liquid-crystal displays that need not undergo a rubbing process during manufacture.The Kerr effect is the development of birefringence in an optically isotropic substance, such as a liquid, when the substance is placed in an electric field. The magnitude of the birefringence induced via the Kerr effect, Dn, can be expressed bywhere Dn is the induced birefringence, k is the wavelength of light, and K is the Kerr constant. The Kerr cell, which is used as an optical shutter, consists of a Kerr substance (usually a polar, organic liquid) placed in an insulating container with two electrodes. This is positioned between crossed linear polarizers whose transmission axes are at ±45 to the applied electric field. In order to obtain the half-wavelength retardation at which maximum contrast can be obtained, the cell needs to have a thickness (optical path length), d k/2 , ofFor example, a Kerr cell containing nitrobenzene, which is generally known to have a very large Kerr constant (K = 2.2 10 ±12 m V ±2 ), [1] requires a cell thickness of about 45 mm for application of an electric field, E, of strength E = 5 10 6 V m ±1 . Fast optical shutters can be used in flat-panel liquid-crystal displays, as these displays consist of arrays of small light shutters. However, Kerr shutters made of nitrobenzene are too thick to be used. Blue phases are liquid-crystalline phases that appear in a very small temperature range between the cholesteric phase (Ch) and the isotropic phase (Iso).[2±5] There are three types of blue phasesÐBPI, BPII, and BPIII. The BPI and BPII phases are characterized by cubic symmetry of the director field, with lattice constants that are comparable to the wavelength of visible light. [6,7] Since blue phases are optically isotropic in zero electric field due to their structural symmetry, surface treatment to obtain a specific molecular orientation, e.g., rubbing to obtain twisted alignment, is redundant. This is a great advantage for device fabrication, because the rubbing process introduces degradation of the display quality and increases manufacturing costs. Recently, we reported that the temperature range over which BPI exists, usually a few degrees Kelvin, was successfully extended to more than 100 K in the polymer±liquid crystal (blue phase) composite system, referred to as the ªpolymer-stabilized blue phaseº. [8,9] In this study, the Kerr effe...